PROJECT SUMMARY/ABSTRACT Drug addiction is a prevalent and chronically relapsing disorder that affects millions of Americans. Our laboratory has recently developed a behavioral economics (BE) paradigm that determines individual motivation for cocaine and propensity for drug relapse in a single testing session. In this paradigm, the neuropeptide orexin (also called hypocretin) is involved in driving motivation for cocaine. Lateral hypothalamus (LH) orexin neurons are highly associated with motivation for reward and project to numerous reward-associated brain regions. However, it remains unclear how LH orexin neurons are recruited to drive motivation for cocaine. Rostral lateral septum (LS) strongly innervates the LH orexin cell field and has been linked to orexin- dependent, stimulus-associated cocaine seeking. The ability of orexin to drive motivation for cocaine also may involve its extensive projections to ventral tegmental area (VTA), a region highly implicated in reward, motivation, and drug addiction. Using a within-session BE paradigm, this proposal will explore the role of LS inputs to LH orexin neurons and LH orexin projections to VTA DA neurons in demand for cocaine. I predict that both of these projections will be necessary for cocaine demand in the BE paradigm. This hypothesis will be tested using three Specific Aims. Aim 1 will determine individual differences in neuronal activity of the LS-LH orexin and LH orexin-VTA circuits using retrograde tract tracing combined with Fos staining in both LS projections to LH, and LH projections to VTA following BE. Aim 2 will utilize pharmacological and morpholino antisense approaches to specifically inhibit the LS-LH orexin circuit and determine its role in cocaine demand. Aim 3 will combine pharmacological, antisense, and chemogenetic approaches to inhibit LH orexin input to VTA DA neurons during BE performance. Together, these studies will elucidate the inputs and outputs of LH orexin neurons involved in cocaine demand to uncover neuropathology underlying drug addiction. This fellowship will train the applicant in several innovative techniques in systems and behavioral neuroscience, including chemogenetic, pharmacological, and antisense manipulations; drug self-administration and behavioral economics paradigms; cannulae and catheter surgeries; and immunohistochemical procedures.